ANKARA (Reuters) - Turkey's banking regulator urged the public on Saturday to ignore rumors about financial institutions, in an apparent dismissal of a report that some Turkish banks face billions of dollars of U.S. fines over alleged violations of Iran sanctions.

"It has been brought to the public's attention that stories, that are rumors in nature, about our banks are not based on documents or facts, and should not be heeded," the BDDK banking regulator said in a statement, adding that Turkey's banks were functioning well.

The Haberturk newspaper on Saturday reported that six banks potentially face substantial fines, citing senior banking sources. It did not name the banks. One bank faces a penalty in excess of $5 billion, while the rest of the fines will be lower, it said.

Asked to comment, a spokesman for the U.S. Treasury, which is responsible for U.S. sanctions regimes, said only: ”Treasury doesn’t telegraph intentions or prospective actions.”

Two senior Turkish economy officials told Reuters Turkey has not received any notice from Washington about such penalties, adding that U.S. regulators would normally inform the finance ministry's financial crimes investigation board.

U.S. authorities have hit global banks with billions of dollars in fines over violations of sanctions with Iran and other countries in recent years.

The administration of U.S. President Donald Trump last week adopted a harsh new approach to Iran by refusing to certify its compliance with a nuclear deal struck with the United States and five other powers including Britain, France and Germany under his predecessor Barack Obama.

Trump argues the deal was too lenient and has effectively left its fate up to the U.S. Congress, which might try to modify it or bring back U.S. sanctions previously imposed on Iran.

Last week, the U.S. Treasury Under Secretary for Terrorism and Financial Intelligence Sigal Mandelker said Trump's strategy involved placing additional sanctions on Tehran and that Washington had been "engaging our allies and partners" with the aim of denying funds to Iran's Revolutionary Guard Corps.

The Haberturk report comes as relations between Washington and Ankara, which are NATO allies, have been strained by a series of diplomatic rows, prompting both countries to cut back issuing visas to each other's citizens.

U.S. prosecutors last month charged a former Turkish economy minister and the ex-head of a state-owned bank with conspiring to violate Iran sanctions by illegally moving hundreds of millions of dollars through the U.S. financial system on Tehran's behalf.

President Tayyip Erdogan has dismissed the charges as politically motivated, and tantamount to an attack on the Turkish Republic.

The charges stem from the case against Reza Zarrab, a wealthy Turkish-Iranian gold trader who was arrested in the United States over sanctions evasion last year. Erdogan has said U.S. authorities had "ulterior motives" in charging Zarrab, who has pleaded not guilty.

(Additional reporting by Ebru Tuncay, Tuvan Gumrukcu and Dirimcan Barut in Turkey and David Brunnstrom in Washington; Writing by David Dolan; Editing by Ros Russell and James Dalgleish)